Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write.
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. Referring now to FIG. 1, the head disk assembly 100 includes at least one disk 102 (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor 104 for rotating the disk, a ramp 116, and a head stack assembly (HSA) 106. The spindle motor typically includes a rotating hub on which disks mounted and clamped, a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle motor and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host. The head stack assembly 106 typically includes an actuator, at least one head gimbal assembly (HGA) 108 that includes a head, and a flex cable assembly 110.
During operation of the disk drive, the actuator must rotate to position the heads adjacent desired information tracks on the disk. The actuator includes a pivot bearing cartridge 112 to facilitate such rotational positioning. One or more actuator arms extend from the actuator body. An actuator coil 114 is supported by the actuator body opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator. A crash stop is typically provided to limit rotation of the actuator in a given direction, and a latch is typically provided to prevent rotation of the actuator when the disk dive is not in use.
In a magnetic hard disk drive, the head typically comprises a body called a “slider” that carries a magnetic transducer on its trailing end. The magnetic transducer typically comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive. In a magnetic hard disk drive, the transducer is typically supported in very close proximity to the magnetic disk by a hydrodynamic air bearing. As the motor rotates the magnetic disk, the hydrodynamic air bearing is formed between an air bearing surface of the slider of the head, and a surface of the magnetic disk. The thickness of the air bearing at the location of the transducer is commonly referred to as “flying height.”
Magnetic hard disk drives are not the only type of information storage devices that have utilized air bearing sliders. For example, air bearing sliders have also been used in optical information storage devices to position a mirror and an objective lens for focusing laser light on the surface of disk media that is not necessarily magnetic.
The flying height is a key parameter that affects the performance of an information storage device. Accordingly, the nominal flying height is typically chosen as a careful compromise between each extreme in a classic engineering “trade-off.” If the flying height is too high, the ability of the transducer to write and/or read information to/from the disk surface is degraded. Therefore, reductions in flying height can facilitate desirable increases in the areal density of data stored on a disk surface. However, the air bearing between the slider and the disk surface can not be eliminated entirely because the air bearing serves to reduce friction and wear (between the slider and the disk surface) to an acceptable level. Excessive reduction in the nominal flying height degrades the tribological performance of the disk drive to the point where the disk drive's lifetime and reliability become unacceptable.
One way that a disk drive designer can improve the prospects of reaching an acceptable compromise in the “trade-off” described above, is to increase the complexity of the disk drive so as to dynamically control flying height. That is, additional head components and/or disk drive components, such as a transducer heater, are included and actively controlled so that the flying height can be temporarily reduced only while the head is reading or writing. When the head is not reading or writing, it can “fly” at a slightly-higher nominal flying height to improve tribological performance. Such active control of flying height is sometimes referred to as “dynamic flying height” control (a.k.a. “DFH”).
If a transducer heater is used to accomplish DFH control via thermal expansion of the head near the transducer, such thermal expansion can also temporarily and locally change the air bearing design. However, the flying height, and therefore the spacing between the transducer or objective lens and the disk surface, depends strongly on the design of the air bearing surface. Temporary and local changes in the air bearing surface design can hinder DFH control by opposing the effect of the transducer heater.
Accordingly, what is needed in the art is an air bearing design that is less sensitive to the thermal expansion associated with the use of a transducer heater to accomplish DFH control.